When an airplane is parked on the ground in order to undergo clearing or maintenance operations, some of its components have to be blocked or clamped mechanically in order to avoid untimely actuation thereof, due to a human mistake or failure of a control system. It is known in particular to immobilize the landing gear of an airplane for maintenance or handling needs on the ground. For this purpose, conventionally steel pins or collars are used, which enable locking of the movable parts of the landing gear, e.g. mechanical hinges or extended landing gear actuators. Such locking devices on the ground are generally equipped with visual identification signs, such as bright colored flags or pennants, so as to be easily spotted by the ground personnel. As a matter of fact, it is mandatory to release the movable parts before take-off, otherwise serious incidents may happen in flight. In spite of precautions taken and a systematic check-up, it still happens regularly that landing gear locking devices are not removed at the pre-flight inspection. If the landing gear cannot be raised, the plane has to return immediately to its departure airport. It is estimated that about 11% of returns to the departure airport, associated with a landing gear problem, are due to a forgotten locking device. Each return implies previously dumping kerosene in order to reduce the weight of the plane below the maximum weight admitted for landing. Such an operation is particularly harmful for the environment and costly, both in terms of fuel and grounding.
Among the causes identified as having led to a forgotten locking device, in particular damaged or missing visual identification signs have been noted. As a matter of fact, flags or pennants can get loose due to wear or incorrect handling, or else they can get stuck in an adjacent part due to the wind, thus hiding from the ground personnel's view.
In order to make them easier to spot, locking devices are sometimes painted in a bright color. However, paints are rapidly eroded by the phosphorus esters existing in most hydraulic fluids, so that locking devices may go unnoticed, in particular under conditions of bad lighting or poor visibility.
A first objective of the invention is to propose a locking device the presence of which can be detected easily and rapidly. A second objective of the invention is to provide a locking device on the ground, which can be detected with very high reliability. A third objective of the invention is to provide a system for automatically detecting said locking devices.